When using Pro Razor, the best technique is to move vertically or side to side in a straight line to make sure you do not miss any algae spots on the aquarium glass. When being thorough in removing algae from the glass, go back over the same spots or any missed spots at a diagonal angle. This speeds up the cleaning process of the glass.
Additionally, it is recommended for you to scrape the algae off the glass when the filter is turned off, right before the water change. This way residual algae that is removed from the glass does not go into the filter and seed the rest of the aquarium with more algae. When you drain the water from the aquarium, try to use the suction hose to suck up any algae now floating around in the aquarium.